Analysis and Study of Mathematical Models for Rwa Problem in Optical Networks

Blocking probability has been one of the key performance to solve Routing and Wavelength Assignment problem (RWA) indexes in the design of wavelength-routed all-optical WDM networks. To evaluate blocking probability different analytical model are introduced. Simulation results on different network topologies and routing policies considered demonstrate that the simulation results match closely with the blocking probabilities computed by our methods for different multiclass call traffic loading scenarios. KeywordsBlocking probability, RWA, optical WDM networks, throughput, performance evaluation I. NTRODUCTION Optical networking has been making rapid advances in recent history. It pays a key role in today’s Internet. They provide huge capacity through fiber links. During the last decades, Wavelength Division Multiplexing (WDM) Optical Networks have emerged as an attractive architecture for backbone networks. WDM networks provide high bandwidth, on the order of tens of Gigabits per second per channel. Hence All-Optical networks based on WDM using wavelength routing techniques is considered as a very promising approach for the realization of future large bandwidth networks. However recently two observations are driving the research community to explore the traffic grooming problem in WDM networks. First, the bandwidth requirements of most of the current applications are just a fraction of the bandwidth offered by a single wavelength in WDM networks. Second, the dominant cost factor in WDM networks is not the number of wavelengths but rather than the network components. The blocking problem is referred as Routing and Wavelength Assignment problem (RWA). There are many wavelength assignment algorithms and analytical model which helps in reducing the blocking probability. This paper is organised in four sections. Introduction on optical network and RWA problem is presented in section I. Section II describes the overview of related work done regarding RWA problem in optical networks and its related research papers. Section III describes the analysis of analytical models to analysis the blocking probability in different networks. Finally conclusion is given in section IV. II. LITERATURE SURVEY Kalyan Kuppuswamy et al. [1] developed an analytical methodology for computing approximate blocking probabilities for multiclass services in optical WDM networks with wavelength continuity constraints. The knapsack approximation used in computing the probability distribution of the no. of the idle wavelength on links and applied this methodology to the three dynamic RWA policiesFR, LLR and FAR all with random wavelength selection. In addition the methodology adds some analytic insights. In analysis it is observed that the per-class pairwise approximate blocking probability for the FR policy can be decomposed as a sum of two terms: one that represent blocking probability with no wavelength continuity constraints and other with the wavelength continuity constraints. Ding Zhemin et al. [2] designed a framework based on blocking island (BI) to solve the problems of placement of wavelength converters (WC) as well as RWA in all optical networks. A simple heuristic for the placement of WCs in an arbitrary mesh network and a general RWA algorithm have been proposed. The proposed algorithms and analytical models also helps to solve various additional problems including traffic grooming, Optical traffic engineering, and network failure allocation. Jong-Seon Kim et al. [3] proposed three dynamic RWA algorithms-named F (w, l), MCR, and LSNLR which make a routing decision on the basis of per-route status then subsequently choose a wavelength and also selects the set of predetermined routes which results in significantly lower blocking probabilities than the shortest-route-based method also requires much less online computation for call processing than well-known algorithms such as SPREAD. In particular algorithm F (w, l) significantly outperforms other existing algorithms in terms of blocking and also requires much less online computation for call processing. Yvan Pointurier et al. [4] presented two classes of adaptive Quality of Transmission (QoT)-aware RWA algorithms for networks with physical impairments. The proposed RWA algorithms can sharply decrease the blocking probability, increase QoT & fairness, low bit error rate (BER) and also mitigate crosstalk effects in comparison with traditional algorithms even when the networks are large and heavily loaded. Jijun Zhao et al. [5] proposed a bidirectional Quality of Service (QoS) differentiation framework that allows to simultaneously consider both the PLIs and the set up delay, giving rise to the design of our ISD-RWA algorithm. The results showed that this algorithm performs 45 ICRTEDC -2014 well in different network topologies and reduces the blocking probability of the transparent optical networks significantly. Ling Li et al. [6] proposed two new dynamic routing algorithms based on path and neighborhood link congestion in all-optical wavelength-routed networks. The fixed-paths least congestion (FPLC) routing used with the first fit wavelength-assignment methods to achieve good performance. The routing using neighborhood information algorithm employed as a trade-off between network performance in terms of blocking probability versus set up delay and control overhead. Shizhong Xu et al. [7] discussed the RWA problem in multifiber networks. In this, RWA problem reduces to the problem of finding a shortest path by making use of the special structure of layered graph. In this two strategies PACK and SPREAD are proposed for this problem and also used the shortest path algorithm M_Dijkstra based on layered graph. The algorithm used can also effectively deal with the failure of fiber/link and node and thus improves the blocking probability. Xiaowen Chu et al. [8] proposed a new dynamic RWA algorithm, called WLCR-FF algorithm to solve the RWA problem in the presence of wavelength conversion. This algorithm makes a good trade-off between the average route length and the link utilization and also improves the blocking performance when compared with conventional dynamic RWA algorithms. Xi Yang et al. [9] proposed the problem of dynamic routing in translucent WDM optical networks. In this sparse placement of regenerators used to overcome physical impairments and wavelength contention introduced by fully transparent networks. To solve the RWA problem they introduced an intradomain routing algorithm IDDBR which establishes the end-to-end lightpaths crossing multiple domain thus boost efficiency and improves the blocking probability in the network. III.ANALYSIS OF ANALYTICAL MODEL The approximate analytical models developed for the clear channel blocking probability of the network with arbitrary topology, both with or without wavelength translations. The goal of our analysis is to calculate the blocking probability. In order to do analysis the following assumptions are made: 1. The network is connected in an arbitrary topology. Each link has a fixed number of wavelengths. 2. Each station has array of transmitters and receivers, where W is the wavelength carried by the fiber. 3. Point to point traffic is considered. 4. There is no Queuing of connection request. The connection blocked will suddenly be discarded. 5. Link loads are mutually independent. 6. Static Routing and Dynamic Routing both are assumed. Kalyan Kuppuswamy et al. [1] analysed the fixed-point approximate blocking probability computations with different loading scenarios. Blocking probability of the network is compared depending upon the number of channels, number of links and traffic load per link (in Erlang). Ding Zhemin et al. [2] examined the performance of placement of wavelength converters and the performance of the BI-RWA algorithms using the NSFNet. They employed a dynamic traffic model in which calls arrive at each node according to an independent Poisson process with arrival rate . An arriving section is equally likely to be delivered to any node in the network. Jong-Seon Kim et al. [3] evaluated the blocking probabilities of the proposed dynamic RWA algorithms on two network topologies (NSFNET network for irregular as well as regular topology) and analysed the comparison of blocking probability with the traffic load (Erlang) for both uniform and non-uniform traffic distribution. As the load increases the blocking probability also increases. Yuan Pointurier et al. [4] evaluated the QoT-aware adaptive RWA algorithm with optional coding by using NSFNET topology. When optional coding is used and all physical impairments are accounted then blocking probabilities lowered but the crosstalk effects were not completely removed. Jijun Zhao et al. [5] evaluated the performance of the ISDRWA algorithm by using network topologies of the US nation-wide network and the COST 239 network. They analysed the comparison of blocking probability with the network load (Erlang) for dynamic traffic and also considered different connection requests with different QoS levels. Ling Li et al. [6] assessed the accuracy of analytical model and the analytical model is applied to two network topologies, a regular Mesh-Torus network and an irregular NSFNet T1 backbone network. They compared the network blocking probability versus the traffic load per source-destination (s-d) pair for eight wavelengths per link for different correlation models. In both networks the analytical results are good for heavy to moderate load but not for the light traffic load. Shizhong Xu et al. [7] used two dynamic RWA algorithms PACK & SPREAD and then studied the performance of these algorithms on two regular network topologies and two irregular network topologies. The blocking performance of two kinds of networks is studied with respect to load (Erlang). One is the network with even links and other is the network with uneven links. Xiaowen Chu et al. [8] investigated the performance of WLCR-FF algorithm over the other algorithms in 8-node ring topology, 25-node mesh-torus topology and 14-node NSFNET topology. In all simulations, the lightpath connection requests are generated as a Poisson Process and the connection holding time is exponentially distributed. IV.CONCLUSION The performance optimization of all-optical WDM network is necessary because of its increasing demand. Blocking probability effects more on the RWA problem so they analysed the response of blocking probability for varying traffic load (Erlang). The analysis showed that as the load per link increases the blocking probability also increases and the response of wavelength conversions are much better than without wavelength conversions. For lower load values, limited wavelength conversion and full wavelength conversion gives similar results but as load per link increases, sparse wavelength conversion has less blocking as compared to even full wavelength conversion and finally the throughput is also found to be better.